Interaction between walkability and fine particulate matter on risk of ischemic stroke: A prospective cohort study in China

Living in walkable neighborhoods has been reported to be associated with a lower risk of cardiovascular disease. Features of walkable neighborhoods, however, may be related to particulate matter with an aerodynamic diameter ≤2.5 μm (PM₂.₅), which could increase risk of cardiovascular disease. The interaction effect between walkability and PM₂.₅ on risk of ischemic stroke remains to be elucidated. In this study, we recruited a total of 27,375 participants aged ≥40 years from Yinzhou District, Ningbo, Zhejiang Province, China to investigate the associations of walkability and PM₂.₅ with risk of ischemic stroke. We used amenity categories and decay functions to evaluate walkability and high-spatiotemporal-resolution land-use regression models to assess PM₂.₅ concentrations. We used Cox proportional hazards regression models to calculate hazard ratios (HRs) and 95% confidence intervals (CIs). During a median follow-up of 4.08 years, we identified a total of 637 incident cases of ischemic stroke in the entire cohort. Higher walkability was associated with a lower risk of ischemic stroke (quartile, Q4 vs. Q1 walkability: HR = 0.59, 95% CI: 0.47–0.75), whereas PM₂.₅ was positively associated with risk of ischemic stroke (Q4 vs. Q1 PM₂.₅: HR = 1.70, 95% CI: 1.29–2.25). Furthermore, we observed a significant interaction between walkability and PM₂.₅ on risk of ischemic stroke. Walkability was inversely associated with risk of ischemic stroke at lower PM₂.₅ concentrations, but this association was attenuated with increasing PM₂.₅ concentrations. Although walkable neighborhoods appear to decrease the risk of ischemic stroke, benefits may be offset by adverse effects of PM₂.₅ exposure in the most polluted areas. These findings are meaningful for future neighborhood design, air pollution control, and stroke prevention.